1. Field of the Invention
The present invention relates to a data creating method and an ink jet printing apparatus, and more specifically, to the formation of an image which is carried out by ejecting a combination of inks such as a black ink and color inks which exhibit different levels of permeability for print media and similarly to the formation of an image which is carried out by allowing color inks to react with a black ink to coagulate the black ink.
2. Description of the Related Art
An ink jet printing method and apparatus for printing various print media have prevailed as output means for various apparatuses such as personal computers because the method and apparatus enables dense and fast printing operations.
The ink jet printing apparatus generally comprises a carriage on which a print head and ink tanks are mounted, conveying means for conveying a print medium such as a print paper and a printable disk, and control means for controlling the carriage and the conveying means. Serial scan is carried out by moving the print head that ejects ink droplets, in a direction (main scanning direction) orthogonal to one (sub-scanning direction) in which the print medium is conveyed, while ejecting ink from a plurality of ejection openings in the print head. On the other hand, during non-printing, the print medium is intermittently conveyed by an amount equal to a print width.
The ink jet printing apparatus carries out printing by ejecting ink to a print medium in accordance with a print signal. Further, the apparatus need not be complicated and thus requires only a low running cost. The ink jet printing apparatus is also known to operate quietly.
In recent years, many products have been put to practical use which can deal with color printing by using a plurality of color inks.
With such a color ink jet printing apparatus that can deal with color printing, for black ink often used to print characters and the like, it is necessary to provide sharp and clear printing and a high print density. As means for achieving this, a technique is known which lowers the permeability of the black ink for print media to suppress the permeation, through print media, of a color material contained in the black ink. On the other hand, concerning color inks, when two different color inks are applied to print media so as to lie adjacent to each other on the media, the inks may be mixed together at their boundary to degrade color images (bleeding). A technique is thus known which lowers the permeability of the color inks for the print media to prevent the inks from being mixed together on the surfaces of the print media, thus preventing the bleeding (see Japanese Patent Application Laid-Open No. 7-047762).
However, if an ink jet is used which includes such a low-permeability black ink and high-permeability color inks, the color inks permeate well and require a relatively short time for fixation. In contrast, the black ink does not permeate well and thus requires a relatively long time for drying and fixation.
Accordingly, when two print media are consecutively printed and discharged, the second print medium may be discharged before the black ink on the first print medium discharged is completely dried. In this case, a print surface of the first print medium or a back surface of the second print medium may be stained (the phenomenon in which the print surface or the back surface are stained is called “smear”).
This problem may become more serious as print speed increases. That is, a new printing operation cannot be performed before the black ink in an image formed on a discharged print medium is completely dried. To avoid the smear, measures described below have hitherto been taken.
One of the measures is a method of providing a fixer to fix inks to the print surfaces of print media (see Paragraph [0048] in Japanese Patent Application Laid-Open No. 7-047762).
The fixer may be, for example, of a heating type. The heating fixer can substantially perfectly remove the moisture from inks provided. Consequently, the inks can be favorably fixed. However, this requires an increase in the size and cost of the printing apparatus. In other words, it is disadvantageously impossible to achieve a reduction in the size and cost the apparatus, which is a unique advantage of the ink jet printing apparatus. Further, with a serial printer, although print media are intermittently conveyed, the use of the fixer may make the conveyance nonuniform.
A second measure is a method called sheet discharging wait control in which the discharging of print media is temporarily stopped.
According to this method, before a printed first print medium is fully dried, the printing of a second print medium is not started. Alternatively, after the second print medium has been printed, the start of a sheet discharging operation is delayed a certain time.
With this control, the second print medium is discharged after the image formed on the first medium has been fully dried. This makes it possible to restrain the occurrence of smear. However, if such control is performed, a sufficient print speed cannot be ensured.
In particular, recently developed ink jet printing apparatuses can carry out high-speed printing at the rate of 15 to 20 sheets per minute. Accordingly, the print speed is an important factor that characterizes the apparatus. However, the above control may reduce the print speed. This means that the performance of the apparatus may be degraded.
A third measure is a printing method in which high-permeability color inks overlap print areas of a black ink.
As such a method, Japanese Patent Application Laid-Open No. 2003-159827 discloses an ink jet printing method of determining whether or not to apply high-permeability color inks to a predetermined area of a print medium as well as the amount of color inks applied, depending on whether a low-permeability black ink is applied to the predetermined area with a high duty or a low duty. According to this method, the black ink and the color inks may be applied to the print medium in an arbitrary order, but in view of a reduction in the time required to fix the black ink, it is preferable to eject the color inks before the black ink.
In this case, the black ink is printed on a sheet surface wetted with the color inks. Consequently, the black ink is more readily fixed to the sheet surface. It is thus possible to suppress the occurrence of smear.
A fourth measure is a method of using a reactive ink system in which color inks contain a substance that, when mixed with a black ink, reacts with and instantaneously coagulates the black ink.
As such a method, Japanese Patent Application Laid-Open No. 8-281930 discloses an ink jet printing method of using color inks one of which contains a component for coagulating a black ink to improve its rigidity and ejecting the black ink to a part of a print medium to which the color inks have already been ejected. With this method, if the color ink containing the coagulating component is combined with the black ink, the resulting color is black with the tint of the color ink combined with the black ink. Consequently, toning occurs to make the image more blackish. Thus, it is possible to form pixels composed of a combination of another color ink and the black ink.
In this case, the color material of the black ink is coagulated and thus does not permeate through the print medium. Consequently, much of the color material remains on the surface of the print medium. This makes it possible to increase the density of black images. Further, the black ink is more readily fixed to the print medium. This suppresses the occurrence of bleeding and smear.
Not only Japanese Patent Application Laid-Open No. 8-281930 but also Japanese Patent Application Laid-Open No. 2003-159827, described above, disclose the system in which the color ink reacts with the black ink.
With the conventional ink jet printing method of applying the color inks to print areas of the black ink, the occurrence of smear can be sufficiently suppressed. The method also achieves a sufficiently high image grade for that day and age. However, in recent years, with the further advancement of the ink jet printing method, a further improvement in image grade has been desired.
With reference to FIG. 4, description will be given of problems that may occur with the conventional printing method in which the color inks overlap the black ink.
In FIG. 4, reference numeral 41 denotes a mask pattern for a cyan (C) ink. Reference numeral 42 denotes a mask pattern for a magenta (M) ink. Reference numeral 43 denotes a mask pattern for a yellow (Y) ink. Each of these mask patterns are composed of 6 (pixels)×16 (pixels). An AND process is executed on black data and each of these color mask patterns to determine the arrangement of color dots (dot arrangement 44) overlapping a black image area. In the figure, white parts of the mask patterns 41, 42, and 43 correspond to masked portions (non-printed pixels) and contain pixels that do not permit ejection of the inks. On the other hand, parts with slanted and horizontal lines correspond to pixels that permit ejection of the inks (printed pixels). In other words, in the mask patterns 41, 42, and 43, the areas with slanted and horizontal lines which are shown at 411, 422, and 433 correspond to the printed pixels.
When the color inks are ejected by overlapping manner to a black image area, the mask patterns 41, 42, and 43 are arranged repeatedly in the vertical and horizontal directions of the black data to print.
When the mask patterns 41, 42, and 43 are used to apply the color inks, the inks C, M, and Y are applied so as to form a dot arrangement shown in the dot arrangement 44. Specifically, the color inks are ejected by overlapping manner to form C, M, Y, red (R), green (G) blue (B), and process black.
For the areas in the dot arrangement 44 which contain slanted, horizontal lines and their combination, C is formed in the area with left slanted lines (for example, the area 441). M is formed in the area with right slanted lines (for example, the area 442). Y is formed in the area with horizontal lines (for example, the area 443). B is formed in the area with a combination of left and right slanted lines (for example, the area 444). G is formed in the area with a combination of left slanted lines and horizontal lines (for example, the area 445). R is formed in the area with a combination of right slanted lines and horizontal lines (for example, the area 446). K is formed in the area with a combination of left and right slanted lines and horizontal lines (for example, the area 447).
When the dot arrangement 44 is used to elect the color inks by overlapping manner to print areas of the black ink in a solid black image, the color inks may bleed from the periphery of black dots. The bleeding may make the tints C, M, Y, R, G, and B of the color inks outstanding to impair the uniformity of the black color. This may degrade the black image. In particular, with a conventional technique such as the one shown in FIG. 4, the number of areas 447 for process black is relatively smaller than that of other areas (for example, areas 441, 442, 443, or the like). Accordingly, the area 447 for process black is not predominant. Thus, the color ink overlapping area (for example, the area 441, 442, 443, or the like) spreading out from the black image area is easily perceived. This may degrade the black image.
Further, when for example, the area 441 for C and the area 442 for M are adjacent to each other as in the dot arrangement 44, the inks C and M are merged together. The merged inks are likely to shift from an impacting position. As a result, the color inks are likely to spread out from the black area as described above.